A seat lifter device which is used in vertical position adjustment of a vehicle seat is generally provided with a link mechanism which causes a seat to undergo lifting and lowering operations, a pinion gear which meshes with an input gear provided in the link mechanism, and a rotational control device which controls the rotation of the pinion gear. In a case in which the seat lifter device is a manual system seat lifter device, a configuration is adopted in which the vertical position of the seat which is supported by the link mechanism is adjusted by transmitting a drive force which is input to the operation handle to the pinion gear via the rotational control device.
For example, the rotational control device (a clutch unit) of the seat lifter device which is disclosed in JP-A-2013-224692 (Reference 1) is capable of moving the seat in the vertical direction through a pulling up operation or a pushing down operation of the operation handle which is linked to the rotational control device. The rotational control device includes a first meshing member which rotates integrally with the rotating shaft of the pinion gear, and a second meshing member which meshes with the first meshing member. By forming a so-called stepped lock system rotation restriction mechanism which restricts the rotation of the pinion gear through the meshing of the first and the second meshing members, it becomes possible to stably hold the vertical position (a lifting position) of the seat in a state in which the operation handle is not being operated.
A rotational control device of the related art includes a sliding contact member which applies frictional resistance to the rotating shaft through sliding contact with the rotating shaft of the pinion gear. Accordingly, the seat is configured so as to not suddenly move downward due to the seat load, even in a state in which the rotational restriction of the rotation restriction mechanism is released during the operation of the operation handle.
However, in the configuration of the related art, in a case in which the braking force (the holding force) based on the friction resistance is excessive, after operating the operation handle, the rotating shaft of the pinion gear may not be capable of rotating to a position at which the first and second meshing members which form the rotation restriction mechanism correctly mesh. In this case, subsequently, due to vibration and the like, a passenger sitting on the seat may feel uneasy in relation to vibrations and sounds which are generated when the meshing position is shifted.
Meanwhile, in a case in which the braking force which is applied to the rotating shaft is set low in order to avoid shifting the meshing position, when releasing the meshing between the first and second meshing members, the release operation of the meshing members is performed in a state in which a great load is applied to the meshing members. Since an increase in the operation force and generation of a release sound which are associated with performing the release operation of the meshing members in a state in which a great load is applied to the meshing members may become factors in reducing the operational comfort, from this perspective, there is room for further improvement.